Preheat the oven to 425ºF or 220ºC and line a baking sheet with some parchment paper. Set aside.
Mix the plant milk and vinegar in a jar or bowl until well combined. Let the mixture rest at room temperature for at least 5 minutes. After this time, the milk will thicken and curdle.
Cut the vegan butter into small pieces and place it in the freezer for 5 minutes.
In the meantime, add the flour, baking powder, sugar, and salt to a large bowl or in a food processor. Whisk or pulse until combined.
Incorporate the vegan butter and cut into the dry ingredients with a pastry cutter or by pulsing several times in the food processor until coarse crumbs form (see photos above). If you have used a food processor, transfer the mixture to a large bowl.
Add the milk and vinegar mixture and gently stir until almost combined, but do not over mix. The dough will be quite moist and sticky at this point (see photos above).
Transfer the dough to a floured work surface and gently bring it together with generously floured hands. The dough will become sticky as you bring it together. Have extra flour nearby and use it often to flour your hands and work surface, but do not add too much or the vegan biscuits will be dry.
Gently flatten the dough into a ¾ or 1-inch thick rectangle (about 2 to 2.5 cm), then fold one side into the center, and then the other side. Turn the dough horizontally and flatten it into a rectangle again. Repeat this process two more times (see photos above).
Cut into circles using a biscuit cutter, but do not twist the biscuit cutter when pressing down into the dough. Re-roll the scraps until all the dough is used.
Transfer the vegan biscuits to the lined baking sheet and brush the tops with a little bit of soy milk. Then bake for 12-15 minutes or until the tops are golden brown. Be careful not to burn them!